Days are getting longer following winter soltice

December 24, 2013

Since the winter solstice occurred close to noon (12:11 p.m.) on Dec. 21 this year, both Friday and Saturday nights in Tupper lake were the same length, 15 hours and 9 minutes from sunset to sunrise.

Tonight will be more than half a minute shorter.

So the days are getting longer, albeit slowly. Sunset will be almost five minutes later than it was on Dec. 9. However, sunrise is still creeping later. The latest sunrise won't occur until Jan. 2 at 7:33:35 a.m. (on a flat horizon), almost two minutes later than this morning's sunrise. So the days for savoring the darkness continue.

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As an astronomer, of course, I am drawn to the night. Many spiritual seekers are also drawn to darkness and silence to look and listen for wisdom. In graduate school, I took to visiting a monastery where the daily prayers began at 4 a.m. There is something sacred in darkness. Perhaps that's why we celebrate the birth of Jesus in this dark season.

Even astronomical objects acknowledge Jesus at this time of year as two symbols of him face each other in the early evenings of December.

In the east, rising an hour-and-a-half after Gemini with Jupiter blazing between the twins, is the constellation of Cancer. The stars of Cancer are fairly faint and arranged in an upside-down Y, as shown in Figure 1. I generally locate Cancer by first finding Gemini, then Leo with its distinctive sickle appearing as a backward question mark, and spotting faint Cancer between them. If you have a dark sky and good eyes (or binoculars), in the center of Cancer is a fuzzy blur of stars known since ancient times. One of the first objects Galileo examined with his telescope, it is a cluster of stars known as the Praesepe, Latin for manger. The two stars to its east are the northern and southern donkeys, Asellus (Ah-SELL-us) Borealis and Australis, nibbling away at the hay. The names for the cluster and stars pre-date the birth of Jesus by centuries, if not millennia, they are not a Christian addition to the sky.

As shown, the Praesepe will be about 20 degrees (twice the width of your fist held at arm's length) above the eastern horizon at 9:15 tonight. This cluster of more than 1,000 gravitationally bound stars is about 20 light years across (a light year is the distance light travels in a year, about 6 trillion miles). At a distance of about 540 light years (so that the light we see today has been traveling since 1543 -?the year Nicolaus Copernicus was born), it covers about a degree and a half in the sky. A familiar sight to Ptolemy, he referred to it as "the nebulous mass in the breast of Cancer." Little did he know that this is a birth group of stars about 600 million years old. Stars form from large, dense molecular clouds such as the one we see as the Great Nebula in Orion. As nuclear explosions contained by gravity, stars continually blow off particles -?protons, helium nuclei and other ions - as stellar winds. These winds eventually clear away the remnants of the cloud, leaving behind a cluster of stars that gradually drift apart. The sun was once in such a cluster, but after 5 billion years of life, its sibling stars have drifted too far away to be identified.

The Praesepe is also known as the Beehive cluster and lies a degree north of the Ecliptic (the plane of the solar system) so planets often appear to move through it. Mars actually passed through its southern reaches last Sept. 8. Jupiter and Venus will follow almost the same path between August 12 and 24, 2014. On August 18, the two planets will be only a quarter of a degree apart and one degree from the center of the star cluster. Unfortunately, this will occur in in the pre-dawn sky with the planets rising at 4:30 am and the sun following an hour and a half later. For the intrepid early risers who watch for the event, with Venus dropping down toward the horizon to meet and pass slower moving Jupiter, it will be a delightful dance to observe.

With an astronomical symbol of Jesus' birth rising in the east, the opposite symbol is on the opposite side of the sky. The Northern Cross, an asterism made up of a portion of Cygnus the swan, appears to stand on the western horizon as the Praesepe rises in the east. Thus the full span of Jesus' Earthly life appears in the sky tonight.

As shown in Figure 2, at 9:15 p.m., bright Vega will barely be visible above a low western horizon. Above it, slightly dimmer Deneb (DEN-ebb), marks the top of the cross. Though it appears about as bright as Vega, it is a truly giant star blazing 55,000 times brighter than the sun at an astounding distance of 1425 light years. The light you see from Deneb tonight left the star in the year 588!

The Northern Cross is large, with the vertical line stretching 22 degrees from Deneb through Sadr (SAD-der) to Alberio (Al-BEER-ee-oh). The horizontal arm of the cross passes through Sadr. Extending it to the next stars on either side, the crooked wings of the swan with Deneb as its tail and Alberio as its beak show it flying along the Milky Way, headed south for the winter.

If the skies are clear tonight and you head out to church services or family gatherings, or remain at home with your friends and loved ones, take a moment to step outdoors and gaze at the astronomical symbols of the life of Jesus. To Christians, his birth, his death and his rising were cosmic events, so it is fitting to find them in the sky, particularly on this Christmas Eve night.

With our roll-off-roof facility up and running, astronomers of the Adirondack Public Observatory are eager to dazzle you with telescopic views of the cosmos every other Friday night (next on Jan. 3). Go to the APO website at apobservatory.org and click on "events" for more information and directions to our site above Little Wolf Pond in Tupper Lake. Listen for me on North Country Public Radio about once a month during "The Eight O'Clock Hour," or email me with any questions at aodonoghue@stlawu.edu.